Field of the Invention
This invention lies in the automotive arts. Specifically, the invention pertains to an antilock braking system, in which an actuator in a braking system is controlled using a number of speed values and pressure values, with the aid of a fuzzy controller.
New requirements in the braking functions, and the requirement to reduce the assembly and maintenance costs, lead to new braking systems in which the force is no longer produced by a braking-torque requirement which originates from the driver and is transmitted directly as a force via a hydraulic system. Instead, an electromechanical brake actuator is controlled with the aid of an electric signal and produces a frictional force on a brake by means of an electrical power supply. This recent advance is generally referred to as a brake-by-wire braking system. Even in such an electromechanical braking system, a device is expedient which prevents the locking of a braked wheel and thus maintains the driving stability of the braked wheel. For this purpose, wheel-speed sensor devices for each wheel or for each group of wheels, and electric, continuously setting braking-pressure or braking-force actuators, which can set an independent braking pressure or an independent braking force for each wheel or for each wheel group, are needed.
Each wheel has an associated wheel-speed sensor which transmits a wheel-speed signal to the computing unit and the control unit. These wheel speeds are used in a conventional computation of the wheel slip in that, for example, a vehicle reference speed is determined from the quickest, non-driven wheel, taking into account steering lock. The slip of a wheel is calculated from the ratio between the measured wheel speed and the vehicle reference speed. If the reference brake pressure requested by the driver exceeds a specific value, which depends on the roadway surface, the affected wheel would lock. This is undesirable, for obvious reasons. It is therefore necessary for the reference pressure to be reduced such that locking of the wheel no longer takes place.
U.S. Pat. No. 4,842,342 to Takahashi et al. discloses an ABS system based on a fuzzy controller, in which the braking force of a hydraulic braking system is controlled from wheel speed values and vehicle acceleration values, with the aid of a fuzzy controller.
U.S. Pat. No. 5,001,640 to Matsumoto et al. discloses an antilock braking system based on a fuzzy controller in which, in addition to speed values, the hydraulic pressure required by an electronic control unit is used to control the braking pressure.
The prior art systems of this generic type are generally complicated and require considerable outlay in computing power and electromechanical control systems.